MMD probabilities

Hello, After giving birth to 3 daughters, my sister-in-law was diagnosed with myatonic muscular dystrophy. So were two of her three sisters, and 2 of her 3 daughters. My sister-in-law, and her sisters,of course, have the adult onset, and her two daughters have the congenital form. The adult sisters are suffering the horrendous affects with falls, broken bones, dangers from surgery, etc.

My 9 yr old niece has some learning disabilites and myatonia affecting her hands all ready. My 7 yr old niece was born with club feet, swallowing difficulties, is mentally impaired, and has many more problems than her older sister. Her life is difficult. They have a 5 yr old sister. Their neurologist says that she does not have MMD, and we would all agree. She beams with joy and laughter.

My questions are:

#1. What are the chances that the 5 yr old will develop the adult onset of this disease?

#2. Even if she never has any form of the disease, is there still a 50/50 chance that she could pass MMD on to her children?

#3. Would genetic testing as an adult tell her if she could have children without passing MMD to them, since the disease seems to worsen with each generation?

Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.

Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.

Myotonic dystrophy (type I) is located on chromosome 19 where a sequence is encoded. This sequence can be normally repeated 5-30 times without noticeable effects. However, if the sequence is repeated hundreds to thousands of times, the symptoms and signs, as you are aware of, will develop. In general, the more repeated sequences, the more severe the illness will be. Also, children of women who have longer sequences will have more severe symptoms than those from mothers with shorter sequences. With each generation, the repeated sequences will grow which leads to earlier and more severe symptoms.

Regarding your questions on chances of developing myotonic dystrophy or having a child with myotonic dystrophy, I would suggest you sister in law talk to a geneticist.

Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.

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